This invention relates to circuit interrupters and more particularly to improvements in an operating mechanism of circuit interrupters.
West German Pat. No. 19 04 731 discloses an electric circuit interrupter in which a movable contact arm having a movable contact is pivoted for opening and closing operation of the circuit interrupter, and the movable contact arm has pivotally mounted thereon a releasable member which is acted by an electromagnetic trip device or a bimetallic thermal trip device to be released for a contact opening operation from the latching action of a latch member. The latching member is pivoted on the movable contact arm with its one end being in the latching engagement with the releasable member and another end thereof is pivotally connected to one end of a toggle mechanism. The other end of the toggle mechanism is pivotally connected to a manually operable operating handle.
When an overcurrent flows through the circuit interrupter, the bimetallic element is heated to deflect to such an extent that the free end of the bimetallic element pushes and rotates the releasable member which in turn releases the latch member from its latching position. As a result, the movable contact arm is pivoted to trip open the circuit interrupter. When a massive overload current much greater than the first overcurrent flows through the circuit interrupter, in addition to the above-described opening operation due to the deflection of the bimetal element the electromagnetic trip device generates an electromagnetic force which actuates a magnetic plunger to push and rotate the latch member from its latching position into its tripping position, which causes the contact opening operation of the circuit interrupter. When it is desired to manually operate the circuit interrupter, the operating handle of the interrupter is moved. When the handle is operated, the toggle mechanism bridging between the handle and the latch member transmits the handling movement to the latch member and to the movable contact arm to open pivot and the contact of the circuit interrupter.
While this circuit interrupter is quite satisfactory in so far as its operation is concerned, it is desirable to provide a circuit interrupter having an operating mechanism simpler in structure for opening and closing the circuit interrupter contacts. A simple operating mechanism results in a superior interrupting capability and ease in manufacture due to the reduced number of parts constituting the operating mechanism.
In copending U.S. patent application Ser. No. 689,435 filed by the same assignee of the present invention, a new circuit interrupter is proposed which is simple in structure and has improved interrupting capability. According to that application, a circuit interrupter comprises a pair of separable contacts at least one of which is movable, and an operating mechanism operably connected to the movable contacts for opening and closing the contacts. The operating mechanism includes a movable contact arm having mounted thereon the movable contact, a latch member pivotally mounted on the movable contact arm, and a toggle link mechanism connected at its one end to an operating handle and the other end of which is directly engageable with said movable contact arm and the latch member. The movable contact arm has a latch surface, and the latch member has a latching end which, in cooperation with the latch surface, releasably catches the other end of the toggle link mechanism.
However, when the operating mechanism is tripped by an over current when the contacts are welded to each other for some reason, the latch lever pivots relative to the movable contact arm while the latter is rigidly held in the closed position. This pivoting movement of the latch lever permits the toggle link mechanism to collapse to rotate the operating handle in a position similar to its contact open position. Also, when the operating handle is manually rotated into the contact open position from the contact closed position with the contacts welded to each other, the toggle link mechanism can be collapsed to pull the latching end of the latch lever to separate from the latch surface of the movable contact arm and yet leave the movable contact arm in the closed position due to welding. This may be disadvantageous in that the operating handle can be positioned in the contact open position even when the contacts are actually closed, posing the danger of causing electrical shocks during maintenance and inspection.